Sơn Đoòng cave is a cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch District, Quảng Bình Province, Vietnam. Currently the biggest known cave in the world, the cave is located near the Laos–Vietnam border (17°27’25.88″N 106°17’15.36″E). Inside is a large, fast-flowing underground river.
Sơn Đoòng Cave was found by a local man named Hồ-Khanh in 1991. The local men were afraid of the cave for the whistling sound caused by an underground river. It was not until 2009 that it became public knowledge after a group of scientists from the British Cave Research Association, led by Howard and Deb Limbert, conducted a survey in Phong Nha-Kẻ Bàng from 10 to 14 April, 2009. Their progress was stopped by a large calcite wall.
According to the Limberts the cave is five times larger than the Phong Nha Cave, previously considered the biggest cave in Vietnam. The biggest chamber of Sơn Đoòng is more than five kilometres long, 200 metres high and 150 metres wide. With these dimensions, Sơn Đoòng overtakes Deer Cave in Malaysia to take the title of the world’s largest cave.
An exit from the cave was found in 2010. The group that scaled the 200 metre high wall found cave pearls the size of baseballs, an abnormally large size.